Non linear and service to failure analysis of sections with evolutional construction working under flexocompresion state

La visión integral de una estructura pasa por reconocer y comprender que ésta sufre durante su construcción, vida útil y desmantelamiento cambios en las condiciones de vinculación, configuración de la sección resistente, aparición de nuevas cargas y materiales... Todo ello complica el cálculo y el análsis de la misma, más aún cuando se consideran los fenómenos diferidos que pueden sufrir materiales como el hormigón y el acero activo así como sus no linealidades. De este modo, el correcto estudio de las estructuras debe abarcar desde su comportamiento a temprana edad hasta su ruina. El análisis en servicio y rotura de las estructuras pasa por el cumplimiento de una serie de recomendaciones recogidas en los códigos actuales sancionados por la práctica. En éstos se hallan los modelos y bases de cálculo necesarios para abordar el problema, no obstante, en muchos casos debe simplificarse enormemente el análsis para poderlo materializar. Consecuentemente, deben eludirse algunos de los principales fenómenos y utilizar modelos que no contemplan lo que realmente sucede y, por lo tanto, debe acudirse al uso de coeficientes de seguridad para el cumplimiento de los requisitos mínimos. No obstante, en numerosas ocasiones, esta estrategia no conduce a soluciones óptimas desde el punto de vista económico porque estos modelos de cálculo simplificados no permiten el máximo rendimiento del material ni reflejan la realidad de un problema tan complejo. En estos casos se recomienda acudir a esquemas de cálculo y modelos más sofisticados dirigidos al empleo de ordenadores y que contemplen la problemática de forma más fidedigna a la realidad. Hay diversas alternativas: el método del coeficiente de envejecimiento, el de las j’s..., entre éstas los métodos paso a paso son los más generales y los que se reservan para los problemas de mayor envergadura

Non linear and service to failure analysis of sections with evolutional construction working under flexocompresion state

La visión integral de una estructura pasa por reconocer y comprender que ésta sufre durante su construcción, vida útil y desmantelamiento cambios en las condiciones de vinculación, configuración de la sección resistente, aparición de nuevas cargas y materiales... Todo ello complica el cálculo y el análsis de la misma, más aún cuando se consideran los fenómenos diferidos que pueden sufrir materiales como el hormigón y el acero activo así como sus no linealidades. De este modo, el correcto estudio de las estructuras debe abarcar desde su comportamiento a temprana edad hasta su ruina. El análisis en servicio y rotura de las estructuras pasa por el cumplimiento de una serie de recomendaciones recogidas en los códigos actuales sancionados por la práctica. En éstos se hallan los modelos y bases de cálculo necesarios para abordar el problema, no obstante, en muchos casos debe simplificarse enormemente el análsis para poderlo materializar. Consecuentemente, deben eludirse algunos de los principales fenómenos y utilizar modelos que no contemplan lo que realmente sucede y, por lo tanto, debe acudirse al uso de coeficientes de seguridad para el cumplimiento de los requisitos mínimos. No obstante, en numerosas ocasiones, esta estrategia no conduce a soluciones óptimas desde el punto de vista económico porque estos modelos de cálculo simplificados no permiten el máximo rendimiento del material ni reflejan la realidad de un problema tan complejo. En estos casos se recomienda acudir a esquemas de cálculo y modelos más sofisticados dirigidos al empleo de ordenadores y que contemplen la problemática de forma más fidedigna a la realidad. Hay diversas alternativas: el método del coeficiente de envejecimiento, el de las j’s..., entre éstas los métodos paso a paso son los más generales y los que se reservan para los problemas de mayor envergadura

Sustainability applied to prefabrication

Prefabrication has evolved in depth and breadth from its beginnings, bringing many of the advantages of industrialisation to construction, while solving some of the problems that arose in the early years. Today prefabrication, compared to traditional construction methods, and concrete as a material, feature a number of beneficial characteristics. Precast elements are factory made products. The only way to industrialise the construction industry is to shift work from temporary construction sites to modern permanent facilities. Factory production entails rational and efficient manufacturing processes, skilled workers, systematisation of repetitive tasks, and lower labour costs per m² as a result of automated production. Factory products are process-based and lean manufacturing principles are deployed. Automation is gradually being implemented in factories and is already in place in areas such as the preparation of reinforcing steel, mould assembly, concrete casting, and surface finishing on architectural concrete. And other stages in the process are sure to follow. As prefabrication makes optimal use of materials, its potential for savings is much greater than in cast-in-situ construction. Structural performance and durability are also enhanced through design, modern manufacturing equipment and carefully planned working procedures. The environmental burden of prefabrication is mainly the burden caused by the raw materials of concrete (especially production of cement and steel). The environmental burden caused by raw materials is approximately three times larger than that caused by the production process of the elements, as indicated by the examples of environmental product declarations. Also thermal inertia of heavy materials is well known for both in warm and cold climates. Most people have experienced the comfort of coming into a comparatively cool stone building on a hot day in a warm climate. In precast structures several systems have been developed using this characteristic. As there is a Fib Bulletin under preparation in Commission 6 Prefabrication, by the Task Group 6.3 Sustainability, in which both authors are members, the conclusions of this document will be presented including a proposal for an evaluation model that can be applied to precast structures.Postprint (published version

Multicriteria decision-making method for sustainable site location of post-disaster temporary housing in urban areas

Many people lose their homes around the world every year because of natural disasters, such as earthquakes, tsunamis, and hurricanes. In the aftermath of a natural disaster, the displaced people (DP) have to move to temporary housing (TH) and do not have the ability to choose the settlement dimensions, distributions, neighborhood, or other characteristics of their TH. Additionally, post-disaster settlement construction causes neighborhood changes, environmental degradation, and large-scale public expenditures. This paper presents a new model to support decision makers in choosing site locations for TH. The model is capable of determining the optimal site location based on the integration of economic, social, and environmental aspects into the whole life cycle of these houses. The integrated value model for sustainable assessment (MIVES), a multicriteria decision making (MCDM) model, is used to assess the sustainability of the aforementioned aspects, and MIVES includes the value function concept, which permits indicator homogenization by taking into account the satisfaction of the involved stakeholders.Peer ReviewedPostprint (author's final draft

Model Code 2010 creep and shrinkage models extension to recycled aggregate concrete

Recycled aggregate concrete (RAC) produced with recycled concrete aggregate (RCA) is one of the most promising ways of eliminating concrete waste and saving natural resources. However, shrinkage and creep behaviour of RAC, important for serviceability design of reinforced and prestressed concrete structures, are still insufficiently studied and guidelines for RAC serviceability design are still not incorporated into design codes and standards. This study aims to systematize the knowledge gained on RAC shrinkage and creep behaviour thus far and to offer analytic expressions for predicting RAC shrinkage strain and creep coefficient. For this purpose, databases of previously published results on RAC shrinkage and creep were compiled and the results on RAC were analysed relative to companion natural aggregate concrete (NAC). The results showed a systematically higher shrinkage and creep of RAC relative to NAC. Finally, analytic expressions for correction coefficients, dependent on RAC compressive strength and RCA replacement ratio, were formulated for predicting RAC shrinkage strain and creep coefficient using the fib Model Code 2010.This work was supported by the Ministry for Education, Science and Technology, Republic of Serbia under grant number TR 36017 and Spansh Ministerio de Economía, Industra y Competividad under the SAES project BIA2016-78742-C2-1-R. This support is gratefully acknowledgedPostprint (published version

A limit state design approach for hybrid reinforced concrete column-supported flat slabs

Hybrid reinforced technology (combination of steel reinforcing bars and fibers) can be considered as a competitive alternative to the already existing solutions for the construction of column-supported flat slabs. Constructed hybrid-reinforced buildings prove that hybrid solutions have sufficient bearing capacity to maintain structural integrity despite being exposed to high stress levels, thereby providing a beneficial solution in terms of toughness, ductility, and sustainability performance. However, the lack of design-oriented recommendations based on the accepted limit state format for dealing with both serviceability and ultimate limit states slows down the wider implementation of this technology. Considering the above-mentioned, this article presents a simplified design-oriented method that covers the evaluation of the structural response of hybrid reinforced concrete column-supported flat slabs in terms of flexural strength, cracking, and instantaneous deformations. Two hybrid reinforced alternatives for a given flat slab are studied by means of the proposed approach. Furthermore, a nonlinear finite element analysis is carried out in order to evaluate the effectiveness of the developed simplified method. Based on the achieved results, its suitable accuracy and precision can be pointed out. This outcome may motivate current practitioners to consider hybrid reinforced concrete solutions as a possible alternative during the design of residential and office buildings.Departament d'Innovació, Universitats i Empresa, Generalitat de Catalunya, Grant/Award Number: 2018 DI 77; Ministerio de Ciencia e Innovación, Grant/Award Number: CREEF (PID2019-108978RB-C32)Peer ReviewedPostprint (published version

Recycling of macro-synthetic fiber-reinforced concrete and properties of new concretes with recycled aggregate and recovered fibers

The study aims to investigate the feasibility of using recycled aggregate (RA) and recovered fibers (RFs) obtained from recycling polypropylene fiber-reinforced concrete (PPFRC) in new concrete production. The mechanical properties were compared between a parent PPFRC, polypropylene fiber-reinforced recycled aggregate concrete (PPRAC), and recovered polypropylene fiber concrete (Re-PPRFC). All concretes were designed to have the same compressive strength and slump. The parent concrete was produced with 3 and 9 kg/m3 of polypropylene fibers. After recycling, the RA and RF were collected, and new concretes with RA and RF, PPRAC and Re-PPRFC, respectively, were produced with the same fiber content as the parent concretes. Both the compressive and flexural tensile strength (pre- and post-cracking) were characterized and the stress–strain relations derived accordingly. The results obtained for the different concretes were compared, proving that the RA and RF obtained by PPFRC recycling can benefit the design-oriented properties (workability and mechanical performance) of new concretes.This study has received funding from the China Scholarship Council (CSC) grant number 202106930007 and MBCC Group. The APC was waived by the journal.Peer ReviewedPostprint (published version

Systematic review on the creep of fiber-reinforced concrete

Fiber-reinforced concrete (FRC) is increasingly used in structural applications owing to its benefits in terms of toughness, durability, ductility, construction cost and time. However, research on the creep behavior of FRC has not kept pace with other areas such as short-term properties. Therefore, this study aims to present a comprehensive and critical review of literature on the creep properties and behavior of FRC with recommendations for future research. A transparent literature search and filtering methodology were used to identify studies regarding creep on the single fiber level, FRC material level, and level of structural behavior of FRC members. Both experimental and theoretical research are analyzed. The results of the review show that, at the single fiber level, pull-out creep should be considered for steel fiber-reinforced concrete, whereas fiber creep can be a governing design parameter in the case of polymeric fiber reinforced concrete subjected to permanent tensile stresses incompatible with the mechanical time-dependent performance of the fiber. On the material level of FRC, a wide variety of test parameters still hinders the formulation of comprehensive constitutive models that allow proper consideration of the creep in the design of FRC elements. Although significant research remains to be carried out, the experience gained so far confirms that both steel and polymeric fibers can be used as concrete reinforcement provided certain limitations in terms of structural applications are imposed. Finally, by providing recommendations for future research, this study aims to contribute to code development and industry uptake of structural FRC applications.This study has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 836270 and from BASF. This support is gratefully acknowledged. Any opinions, findings, conclusions, and/or recommendations in the paper are those of the authors and do not necessarily represent the views of the individuals or organizations acknowledged. A.d.l.F. has previously received research grants from BASF.Peer ReviewedPostprint (published version

Discussion of the article 'Prediction of creep of recycled aggregate concrete using back-propagation neural network and support vector machine'

In a recent study, Rong et al.1 investigate the prediction of recycled aggregate concrete (RAC) creep using back-propagation neural network and support vector machine. For this purpose, the authors compiled a database of experimental results on the creep of RAC on which they first tested five analytical RAC creep prediction models2-6 and concluded that the performance of all five models is inadequate, thereby justifying the use of a back-propagation neural network and a support vector machine. The main argument for declaring the performance of the five analytical models inadequate is the analysis of “performance indices” of the correlation coefficient (R), mean absolute error (MAE), mean square error (MSE), and integral absolute error (IAE). The found ranges of values were 0.45–0.55 for R, 0.41–0.64 for MAE, 0.33–0.70 for MSE, and 0.33–0.53 for IAE. Nonetheless, there are errors and uncertainties regarding the study that are pointed out herein, some methodological and some formal.Postprint (published version

Sustainability based-approach to determine the concrete type and reinforcement configuration of TBM tunnels linings. Case study: Extension line to Barcelona Airport T1

Fibre-reinforced concrete (FRC) is a suitable alternative to the traditional reinforced concrete used in the manufacture of precast segments used to line tunnels excavated with a tunnel boring machine (TBM). Moreover, its use as a structural material has been approved by several national codes and by the current fib Model Code (2010). The use of FRC in segmental linings confers several technical and economic advantages, evidenced by the fact that structural fibres have been used to partially or entirely replace reinforcing bars in many TBM tunnels built over the past 20 years or currently under construction. FRC could also have been used in other tunnels, which are currently in the planning stage or under construction. However, despite its technical suitability and approval in current codes, the use of FRC was not possible in some cases. The impediment has sometimes been an incomplete understanding of the structural behaviour of the material, but a more general motive has been that comparisons of materials have taken into account only direct material costs and have not considered indirect costs or social and environmental factors. The aim of the present research is to develop a method for analysing the sustainability of different concrete and reinforcement configurations for segmental linings of TBM tunnels using the MIVES method (a multi-criteria decision making approach for assessing sustainability). This MCDM method allows minimising subjectivity in decision making while integrating economic, environmental and social factors. The model has been used to assess the sustainability of different alternatives proposed for manufacturing the segmental tunnel lining for the extension of the rail line of Ferrocarrils de la Generalitat de Catalunya (FGC) to Terminal 1 of El Prat Airport in Barcelona.Peer ReviewedPostprint (author's final draft